1. Field of the Invention
The present invention relates to a process for producing an aluminum sintering and an aluminum-alloy sintering.
2. Description of the Related Art
Powder metallurgy has been well known heretofore as a technology which comprises compression molding a powder of a metal or an alloy and then sintering the resulting molding at a temperature not higher than the melting point of the metal or the alloy.
Powder metallurgy is advantageous in that it directly enables a product to be shaped from a powder without applying additional processing such as cutting or grinding, and that it allows the production of any article having a complicated shape.
Although powder metallurgy has the merits above, it is not always applicable to every type of metallic powder.
Particularly, in case of an aluminum sintering, a stubborn oxide film (Al.sub.2 O.sub.3) generated on the surface of the particles constituting the powder of aluminum or an aluminum alloy. The oxide film (Al.sub.2 O.sub.3) which covers the surface of the particles during the sintering process prevents the atoms of aluminum or an aluminum alloy from strongly bonding with each other.
As a related art process, Japanese patent Laid Open No. Hei6-33164 and Hei6-57363 each disclose a technology for sintering an aluminum alloy powder.
Laid Open No. Hei6-33164 discloses a technology which comprises preparing an aluminum alloy powder containing magnesium, heating the powder in an atmosphere containing nitrogen to form a nitride on the surface portion of the powder, and hot processing the powder having a nitride coating thereon into a product having the desired shape.
According to the technology, an aluminum alloy member having an improved toughness, strength, and wear resistance can be obtained by producing a grain-dispersed aluminum alloy through the process of producing the material using a powder of the aluminum alloy.
According to the technology disclosed in Laid Open No. Hei6-57363, a melt of an aluminum alloy containing magnesium at a predetermined percentage by weight is solidified at a predetermined rate of solidification to obtain a quench-solidified powder of an aluminum alloy, and the resulting powder is subjected to cold compression molding. If necessary, the powder is subjected to annealing in a predetermined temperature range before the cold compression molding. The molding is then sintered under ordinary pressure in an atmosphere containing water vapor and nitrogen each at predetermined partial pressures, and into which a predetermined quantity of a reducing gas is added as a gaseous component which accelerates the formation of a nitrogen compound. In this manner, a compound of nitrogen is formed on the surface of the powder, and a nitrided aluminum-alloy sintering containing from 0.4 to 4.0% by weight of magnesium and from 0.2 to 4.0% by weight of nitrogen is obtained therefrom.
According to the technology above, a sintered aluminum alloy having excellent mechanical properties, physical properties, and wear resistance can be obtained at a high density and precision. Moreover, the alloy can be produced highly economically by normal pressure sintering without applying any plastic processing.
The related art technology described above both comprises forming a nitride (AlN) on the surface of the powder particles of aluminum to increase the sintering density. Although the bonding strength is found to somewhat increase as compared with the case of sintering an aluminum powder having a film of aluminum oxide (Al.sub.2 O.sub.3) on the surface of the particles, it is also found that there is yet more problems to be overcome.
The prevent invention aims to overcome the aforementioned problems.
An object of the present invention is to provide, in producing sinterings of an aluminum powder or an aluminum alloy powder, a process for producing an aluminum sintering in which the bonding strength among the particles of aluminum or an aluminum alloy is increased, yet taking the advantage of a sintering process.